In 2-chamber temperature shock test chambers, condensation on sample surfaces primarily arises from the condensation of water vapor in the ambient air during rapid high-low temperature transitions. When the chamber switches from a high-temperature to a low-temperature phase, the sample surface temperature may be lower than the dew point of the surrounding air, causing water vapor to condense into liquid water on the sample surface. Conversely, during the transition from a low-temperature to a high-temperature phase, residual moisture inside the sample or high humidity within the chamber may cause the moisture to evaporate and then recondense upon cooling. The presence of condensation can affect the sample's electrical properties, mechanical strength, or chemical stability, and may also interfere with the accuracy of subsequent test results. Therefore, systematic design optimization and operational procedures are necessary to avoid this problem.
Sample pretreatment is the primary step in preventing condensation. Samples must be dried before testing to reduce their initial moisture content. For highly hygroscopic materials, such as plastics, rubber, or composite materials, a constant-temperature drying oven can be used to ensure sufficient evaporation of moisture from the sample surface and interior. If the test chamber is equipped with an independent drying/dehumidifying function, it can be run for a period of time before testing, using a circulating air duct to deliver dry air to the test area to further remove residual moisture from the sample surface. Furthermore, for samples with poor sealing, the sealing performance of the outer shell or interfaces should be checked before testing to prevent external moisture from seeping in during the test.
Optimizing the temperature switching strategy can reduce the risk of condensation. Traditional 2-chamber temperature shock test chambers typically use a direct switching between high and low temperatures, but this method easily leads to a sudden change in sample surface temperature, increasing the probability of condensation. Improved methods include setting a "buffer zone" temperature range, for example, when switching from +150℃ to -70℃, first transitioning through an intermediate temperature range (such as +25℃) to allow the sample surface temperature to gradually adapt to the change; or extending the residence time of the sample in the transition zone, using a circulating air duct to allow the sample surface temperature to converge with the ambient temperature inside the chamber before switching. These strategies suppress condensation by slowing the rate of temperature change and reducing the temperature difference between the sample surface and the air.
The performance of the equipment's dehumidification system directly affects condensation control. High-end 2-chamber temperature shock test chambers are typically equipped with high-efficiency dehumidification devices, such as molecular sieve rotary dehumidifiers or condenser dehumidifiers. Molecular sieve rotary dehumidifiers continuously remove water vapor from the air through adsorption materials, maintaining high dehumidification efficiency even at low temperatures; condenser dehumidifiers lower the air temperature below the dew point, causing water vapor to condense and be discharged. Furthermore, the chamber's airflow design must ensure uniform air circulation to avoid excessively high humidity in localized areas. For example, using a honeycomb baffle combined with a long-shaft centrifugal fan can enhance the heat exchange capacity between the airflow and the heater/cooler, improving humidity uniformity within the chamber.
The chamber's airtightness and insulation are crucial to preventing external moisture infiltration. The doors, observation windows, and test ports of the 2-chamber temperature shock test chamber must use silicone rubber sealing strips or airtight structures to ensure no external humid air enters during testing. Meanwhile, the chamber insulation layer must use high-density polyurethane foam or fiberglass material to effectively block the impact of external temperature changes on the internal environment. If the chamber's sealing is insufficient, humid air from outside may rush in rapidly when the door is opened, especially during low-temperature testing, where humid air easily condenses on the sample surface upon cooling.
Proper operating procedures during testing are equally important. When placing or removing samples, the time the chamber door is open should be minimized, and frequent opening and closing of the door should be avoided to reduce the entry of humid air from outside. If test cables need to be connected during testing, they must be accessed through the standard lead-in hole on the top of the chamber, ensuring a good seal. Furthermore, condensate inside the chamber must be cleaned promptly after testing to prevent bacterial growth or corrosion of internal components.
The application of intelligent monitoring systems can provide real-time warnings of condensation risks. Some high-end 2-chamber temperature shock test chambers are equipped with intelligent humidity sensors and dew point temperature monitoring modules, which can display real-time humidity, dew point temperature, and sample surface temperature curves. When the sample surface temperature is detected to be close to the dew point temperature, the system can automatically adjust the temperature switching strategy or activate the auxiliary dehumidification function to prevent condensation in advance. Regular maintenance and calibration are fundamental to ensuring the long-term stable operation of equipment. Components such as the dehumidifier, air ducts, filters, and seals of the test chamber should be inspected regularly to ensure their performance meets requirements. For example, the adsorption material of a molecular sieve rotary dehumidifier needs to be replaced periodically, the condensate drain pipes of a condenser dehumidifier need to be cleaned, and dust in the air ducts should be removed using a vacuum cleaner or compressed air. Furthermore, parameters such as temperature uniformity and humidity control accuracy of the equipment must be calibrated according to standard methods to prevent condensation control failure due to equipment performance degradation.
